The present invention relates to a torus-type apparatus for nuclear fusion. More specifically, the invention relates to a toroidal coil apparatus in which a plurality of coils are arranged in the torus form, and particularly to such a construction for supporting electromagnetic force.
Generally, the torus-type nuclear fusion apparatus consists, as shown in FIGS. 1 and 2, of a plurality of toroidal coils 1 each surrounding a common closed loop axis A, a vacuum container 2, air-core current transformer coils 3, and poloidal coils 4. The vacuum container 2 has a trapezoidal shape or a circular doughnut shape in cross section thereof and a plasma P is confined therein therein by the magnetic field in the toroidal direction, poloidal direction and vertical direction. The toroidal coils 1 have a circular shape or a D-shape to approximate the shape of the plasma P which is heated by an electric current produced by a voltage induced in the plasma P by changing the magnetic flux of the air-core current transformer coils 3 wound in the vicinity of the vacuum container 2.
In a toroidal magnetic field generator of the torus-type nuclear fusion apparatus, in general, heavy currents are permitted to flow in the same direction through a plurality of coils arranged on a torus circle, thereby to generate toroidal magnetic field. An intense electromagnetic force is generated in the toroidal coils owing to the interaction between the magnetic field and coil currents. The electromagnetic force works as an expanding force F to expand the coils in general, and is so distributed as to become intense toward the inner side of the torus and weak toward the outer side of the torus. Therefore, there develops a force (centripetal force) Fr which acts to collect the plurality of toroidal coils to the center as a whole. Further, heavy currents are permitted to flow into the poloidal coils installed adjacent to the toroidal coils to generate a poloidal magnetic field, thereby to heat the plasma, and to control the shape and position of the plasma. Here, the poloidal magnetic field intersects the electric currents flowing through the toroidal coils, whereby a force is generated to invert the toroidal coils outwardly at the surfaces thereof. In the torus-type nuclear fusion apparatus, a problem remains with regard to how to support the electromagnetic force generated in the toroidal coils and how to minimize the stress generated in the toroidal coils.
To cope with this problem, the conventional apparatus has been constructed as shown in FIGS. 3 to 5.
That is, as shown in FIGS. 3 and 4, the toroidal coils 1 each consisting of a conductor wound in a number of turns, are contained in coil support frames 5a, 5b consisting of straight portions 5a, and curved portions 5b connecting opposite ends of the straight portions 5a, and made of a nonmagnetic material such as SUS or a strong aluminum alloy capable of withstanding an intense electromagnetic force generated in the toroidal coils 1. The coil support frames 5a, 5b are strongly fastened at their upper and lower portions to a rack 7 by bolts 8 via coil support legs 6, so as to be capable of withstanding the weights of the toroidal coils 1, heat, electromagnetic force F, centripetal force Fr, and inverting force F.sub.Q. Further, wedge-like coupling portions 5c are provided to support the centripetal force Fr at positions of wedge portions 1a at the inner end portions of toroidal coils 1.
The toroidal coils 1 contained in the coil support frames 5a, 5b are arranged in a plurality of coils in a toroidal direction. Then, a force is applied to the back side of the coils using hydraulic jacks or the like with the coil support frames 5b being located on the center side, in order to collect the toroidal coils 1 in a precise radial form. Then, the coil support legs 6 are fastened and secured to the rack 7 by bolts 8 so that wedge surfaces of the wedge-like coupling portions 5c provided on the inner side of the coil support frames 5a, 5b are intimately contacted with each other, and that the centripetal force Fr is correctly received via the wedge surfaces. Further, the inverting force F.sub.Q illustrated in FIG. 6 is received by inversion preventing beams 9a, 9b which are provided between the coil support frames 5a and 5b as shown in FIG. 5. In recent years, however, an increase in the scale of the apparatus has resulted in the increased intensity of the magnetic fields and increased electromagnetic forces, making it difficult to support the centripetal force Fr and the inverting force F.sub.Q. That is, efforts have been made to maintain the wedge effect against the centripetal force Fr by relying upon the wedge surfaces of the wedge-like coupling portions 5c. However, as the coils are constructed in larger sizes and the total height of the coils becomes large, it becomes difficult to maintain precision while constructing the coils. Therefore, despite the fact that the coils are pushed by hydraulic jacks and are secured by bolts 8, the pushing force Ft for the coils is effective only in the vicinities of coil support legs 6; i.e., it is no longer possible to maintain the pushing force Ft for the total height of the coils. That is, even though the coil support frames 5a, 5b at the upper and lower portions of toroidal coils 1 are pushed by jacks 11, the toroidal coils 1 undergo displacement as shown in FIG. 7. Accordingly, the pushing force is not transmitted to the central and straight portion of the coils, and the wedge effect is not obtained for the total height of the coils.
Japanese Patent Application No. 48315/1979 teaches to provide a cylinder for the straight portion of coil, and to provide a wedge mechanism between the cylinder and the coil frame. According to this method, however, the coil must be constructed in two-split construction so that the cylinder can be inserted. Furthermore, it is difficult to have the wedge mechanism work for the total height, and also it is difficult to adjust for slacks.